The above function was ripped from the latest release which is 0.12.1. It’s not hard to spot that the size calculation in g_malloc() could result in an integer overflow since both ‘width’ and ‘height’ variables are derived from user controlled data. Additionally, pointer ‘surface’ is initialized using cairo_image_surface_create_for_data() which would almost certainly fail if ‘cairo_pixels’ allocation failed in the previous g_malloc(). From its official documentation we can read the following:

The caller owns the surface and should call cairo_surface_destroy() when done with it.
This function always returns a valid pointer, but it will return a pointer to a "nil" surface
in the case of an error such as out of memory or an invalid stride value.

But as you can read in create_surface_from_thumbnail_data() there is no check of the return value of that CAIRO library routine. This issue was fixed by applying Carlos Garcia Campos’ patch:

He removed the ‘key’ static variable and inserted a new integer named ‘cairo_stride’. All of the buggy code was removed and the cairo_image_surface_create() was used to handle the allocation of the image surface. Also, cairo_image_surface_get_data() and cairo_image_surface_get_stride() to obtain a pointer to the data of the passed pointer and retrieve the stride of the image in bytes in order to initialize ‘cairo_stride’. Finally, the following update was changed: